Bash script to add a file by its index to the git staging area.

git-add-by-index.sh

#!/usr/bin/bash

git_status=`git status --porcelain`

if [[ $# -ne 1 ]]
then
  # Get modified files and their index
  # nl: numbers the lines
  echo "$git_status" | nl 
  exit 0
fi

if ! [[ "$1" =~ ^[0-9]+$ ]]
then
  echo "Sorry integers only"
  exit 1
fi

line=`echo "$git_status" | sed "${1}q;d"` 
# remove first 4 chars. E.g. M and some spaces
file=`echo "$line" | cut -c3-`
git add $file
git status -s